The present invention relates generally to injection molding systems which use a heated torpedo disposed in a cavity plate to heat melt flowing from a let injection nozzle through the cavity plate into a mold cavity, and more particularly, to an improved heated torpedo having an integral construction.
Injection molding is widely used for the manufacture of a variety of items. Injection molding is typically performed by injecting heated, liquid melt into either a single mold cavity or into one or more mold bores, each of which feeds a number of mold cavities. In either application, a heated flowpath must be provided to convey the injected, liquid melt from the injection machine to the mold cavities without interruption. It is therefore desirable to provide a constant application of sufficient heat to the melt flow to keep it liquid while it passes through the mold bore under pressure and into the mold cavities. Heated torpedoes are commonly used for this purpose.
Heated torpedoes of two-piece construction typically use a separate torpedo body having an internal heater and a separate torpedo end which are welded together to form the final heated torpedo. In this type of two-piece construction, the weld which joins the torpedo body to the torpedo end is positioned on the exterior heated surface of the torpedo body, in the flow path of the pressurized liquid melt. Such welds must be carefully examined to ensure that no porosity is present which would allow entrance of the liquid, pressurized melt into the internal heater leading to possible contamination and burnout of the same. This problem described is a typical one or two-piece heated torpedo constructions which utilize separate torpedo bodies and ends.
Additionally, in two-piece torpedo constructions, the heating element may not extend for any significant length into the torpedo end. Such torpedoes are likely to have "cold spots", that is, areas on the torpedo surfaces over which the melt passes which have different and lower temperatures. The previous solution to a torpedo end which exhibited "cold spots" was to apply an external band heater. This solution adds to the cost and complexity of the molding operation.
The present invention is directed to an internally heated torpedo of integral construction which avoids the above shortcomings.
In an internally heated torpedo constructed in accordance with the present invention, an elongate torpedo body axially extends from a torpedo end disposed at the melt inlet end of the torpedo and terminates in a tip at the torpedo body melt outlet end. The torpedo body has a central cavity extending axially from near the torpedo body tip to well inside the enlarged end portion which is adapted to receive a heating element and position that heating element in close proximity to the outer surface of the torpedo body. The torpedo enlarged end contains a series of axial melt flow passages disposed around the torpedo body which passages serve to define the extent of the torpedo body within the enlarged end portion. An end cap is provided on the enlarged end portion and defines a melt flow entrance chamber or flow path to the melt flow passages.
Accordingly, it is a general object of the present invention to provide an internally heated torpedo of improved integral construction for use in injection molding systems.
Another object of the present invention is to provide an internally heated torpedo having a torpedo body terminating at one end in a tip and terminating at the other end in a torpedo enlarged end, wherein the torpedo body has an internal electrical heating element which extends axially within the torpedo body between the tip and within the torpedo enlarged end to provide a uniform and effective heated surface the length of the torpedo for melt to flow.
It is another object of the present invention to provide an internally heated torpedo of integral construction for use in injection molding systems wherein the torpedo has an enlarged end portion at its melt inlet end and an elongate torpedo body portion which axially extends from the enlarged end portion and terminates in a tip at the torpedo melt outlet end and wherein the enlarged end portion includes a plurality of melt flow passages axially extending therethrough in close proximity to the internal heater.
It is still another object of the present invention to provide a heated torpedo having a torpedo body which is integral with a torpedo inlet end and having a heater disposed within the torpedo body which extends for substantially the entire length of the torpedo.
It is still another object of the present invention to provide an internally heated torpedo of integral construction for use in injection molding wherein the torpedo has an enlarged torpedo inlet end having means to receive the melt flow from an injection molding nozzle and means to distribute the melt flow over the heated exterior surface of an elongate torpedo body portion to the torpedo outlet end wherein the torpedo body contains an internal electrical heating element which extends axially between the torpedo inlet and outlet ends.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.